The present invention relates to rigid supports for rotating shafts. More particularly, it relates to the application of a rigid support to one end of an axial drive screw in a screw drive telescoping mast.
The present invention is applicable to a screw-driven telescoping mast and will be described with particular reference thereto; however, the invention has much broader applications and may be used in various other applications where a rigid bearing assembly for a rotating shaft is required.
Two important criteria for a telescoping mast are the “nested” or fully retracted height and the “extended” or fully extended height. The nested height is the height of the mast when fully retracted. For a given extended height many factors can affect the nested height. These may include the number of tubes in the mast, the amount of overlap between tubes when extended and the details of the end features (such as collars and bottom structures) on each tube. For screw driven masts an additional factor affecting the mast nested height is the amount of height required for a support for supporting the axial drive screw. It is preferable to minimize the nested height. A smaller nested height helps facilitate integrating the mast in shelters and vehicles where clearance is a concern. Thus, it is preferable to provide a drive screw support which minimizes the nested height of the mast.
Existing rigid supports for rotating shafts use two bearings which are axially spaced along the length of the shaft. This spacing results in a height of the support typically three (3) times the diameter of the shaft or more. Thus, in screw drive mast applications where the screw is has a one (1) inch diameter, the spacing of the axial support would be about three (3) inches. When the thickness of the bearings and the necessary support structures are included, an overall height for the rigid bearing assembly of five (5) or more inches can result. This height proves excessive for many screw drive telescoping mast applications. Thus, this excessive height is a deficiency that the present invention addresses and overcomes.
Some existing screw driven telescoping masts attempt to minimize the vertical space required of the axial screw support bearings by using a single bearing instead of the preferred rigid bearing assembly. This arrangement provides inadequate support to the screw, allowing the screw to wobble during operation, potentially causing damage to the mast. This single bearing scheme is also only workable at all at a slow speed, which is inconvenient for any user and potentially critical for the emergency or military user. Thus, there is a need for a mast telescopic system which overcomes the above-mentioned defects and others while providing more advantageous overall results.